diff options
Diffstat (limited to 'kernel/vdso')
| -rw-r--r-- | kernel/vdso/vdso.c | 75 |
1 files changed, 35 insertions, 40 deletions
diff --git a/kernel/vdso/vdso.c b/kernel/vdso/vdso.c index 79c2f05..6a1c198 100644 --- a/kernel/vdso/vdso.c +++ b/kernel/vdso/vdso.c @@ -10,13 +10,12 @@ /* * In projects like github.com/mssola/fbos I already dealt with ELF parsing - * myself and it was the nicest experience. Plus, in here I have to do some + * myself and it wasn't the nicest experience. Plus, in here I have to do some * heave usage of some ELF sections. For this reason I will not do things * manually and use the standard library instead. */ #include <elf.h> - // Terminate the current program with a failure exit code while also printing // the given `message` into stderr. __attribute__((noreturn)) void die(const char *const message) @@ -47,13 +46,8 @@ bool is_vdso_function(const char *const name) return false; } - return name[0] == '_' && - name[1] == '_' && - name[2] == 'v' && - name[3] == 'd' && - name[4] == 's' && - name[5] == 'o' && - name[6] == '_'; + return name[0] == '_' && name[1] == '_' && name[2] == 'v' && name[3] == 'd' && name[4] == 's' && + name[5] == 'o' && name[6] == '_'; } int main(void) @@ -63,17 +57,17 @@ int main(void) * passed by the kernel to each program in the initial auxiliary vector (see * getauxval(3)), via the AT_SYSINFO_EHDR tag". */ - void *vdso = (void *) getauxval(AT_SYSINFO_EHDR); + void *vdso = (void *)getauxval(AT_SYSINFO_EHDR); if (!vdso) { die("Could not get base address for vDSO\n"); } printf("=> vDSO base address: %pS\n", vdso); // Basic assertion :) - ensure_proper_elf_header((const char *) vdso); + ensure_proper_elf_header((const char *)vdso); // The ELF header is the first thing starting from the fetched address. - const Elf64_Ehdr *ehdr = (const Elf64_Ehdr *) vdso; + const Elf64_Ehdr *ehdr = (const Elf64_Ehdr *)vdso; /* * Grab the base address for the Section Header Table for the ELF @@ -81,56 +75,57 @@ int main(void) * dynamic symbol table and the dynamic string table. This will be used * later for looking up the address for each given function name. */ - const Elf64_Shdr *shdr = (const Elf64_Shdr *)((const char *) vdso + ehdr->e_shoff); - const Elf64_Shdr *symbols_header = NULL; - const Elf64_Shdr *strings_header = NULL; - - for (int i = 0; i < ehdr->e_shnum; i++) { - if (shdr[i].sh_type == SHT_DYNSYM) { - symbols_header = &shdr[i]; - } else if (shdr[i].sh_type == SHT_STRTAB) { - const char *shstrtab = (const char *) vdso + shdr[ehdr->e_shstrndx].sh_offset; - const char *strtab_name = shstrtab + shdr[i].sh_name; - - if (strcmp(strtab_name, ".dynstr") == 0) { - strings_header = &shdr[i]; - } - } - } - if (!symbols_header || !strings_header) { - die("Could not find .dynsym or .dynstr sections\n"); - } + const Elf64_Shdr *shdr = (const Elf64_Shdr *)((const char *)vdso + ehdr->e_shoff); + const Elf64_Shdr *symbols_header = NULL; + const Elf64_Shdr *strings_header = NULL; + + for (int i = 0; i < ehdr->e_shnum; i++) { + if (shdr[i].sh_type == SHT_DYNSYM) { + symbols_header = &shdr[i]; + } else if (shdr[i].sh_type == SHT_STRTAB) { + const char *shstrtab = (const char *)vdso + shdr[ehdr->e_shstrndx].sh_offset; + const char *strtab_name = shstrtab + shdr[i].sh_name; + + if (strcmp(strtab_name, ".dynstr") == 0) { + strings_header = &shdr[i]; + } + } + } + if (!symbols_header || !strings_header) { + die("Could not find .dynsym or .dynstr sections\n"); + } /* * Now that we know where to pick the strings and their corresponding * addresses, let's use their offsets to pair it with the original base * 'vdso' address. This will give us a pointer to the proper tables. */ - const Elf64_Sym *symbols_table = (const Elf64_Sym *)((const char *) vdso + symbols_header->sh_offset); - const char *strings_table = (const char *)((const char *) vdso + strings_header->sh_offset); - int num_symbols = symbols_header->sh_size / symbols_header->sh_entsize; + const Elf64_Sym *symbols_table = + (const Elf64_Sym *)((const char *)vdso + symbols_header->sh_offset); + const char *strings_table = (const char *)((const char *)vdso + strings_header->sh_offset); + int num_symbols = symbols_header->sh_size / symbols_header->sh_entsize; /* * As an example we will find the 'getcpu' system call which is exported on * a Linux x86_64 system. */ - int (*vdso_getcpu)(unsigned int *, unsigned int*) = NULL; + int (*vdso_getcpu)(unsigned int *, unsigned int *) = NULL; printf("=> The following system calls are available via vDSO:\n"); - for (int i = 0; i < num_symbols; i++) { + for (int i = 0; i < num_symbols; i++) { // The name of the function directly sits at the strings table plus the // offset given on the symbols table. - const char *name = strings_table + symbols_table[i].st_name; + const char *name = strings_table + symbols_table[i].st_name; if (is_vdso_function(name)) { - void *address = (void *)((char *) vdso + symbols_table[i].st_value); + void *address = (void *)((char *)vdso + symbols_table[i].st_value); printf("\t%s (address: %p)\n", name, address); if (strcmp(name, "__vdso_getcpu") == 0) { - vdso_getcpu = (int (*)(unsigned int *, unsigned int *)) address; + vdso_getcpu = (int (*)(unsigned int *, unsigned int *))address; } } - } + } /* * As an example, run the 'getcpu' system call via the vDSO mechanism. |